摘要:

We recorded the height of a granitic fault surface as a function of position along one‐dimensional profiles. We show that the profiles exhibit an “anisotropic” scaling invariance:self‐affinity. The difference between the maximum and the minimum height, and the standard deviation of the height, over a lengthLare proportional toLζ, where ζ ≈ 0.84. Other properties such as the Return Probability distribution or the Power Spectrum of the profile comfort this result. This self‐affine property is in good agreement with recent works on artificial fractured surfaces. Previous studies at field scale are consistent with

ISSN:0094-8276    

DOI:10.1029/93GL00170

年代:1993

数据来源: WILEY

摘要:

The behavior of a simple one‐dimensional, homogeneous, deterministic model of an earthquake fault is examined on the timescale of the rupture process. The model generates a complex spatial and temporal distribution of events from a frictional instability. I measure the frequency spectra of the moment release rate for events of different sizes, and observe power laws for the spectra. A bend in the spectra of large events is also observed. The paper concludes with a discussion of how these results may be relevant to real earthquake fault

ISSN:0094-8276    

DOI:10.1029/92GL02437

年代:1993

数据来源: WILEY

摘要:

We have modeled displacement time histories to infer the large‐scale rupture process of the 28 June 1992M7.4 Landers, California, earthquake. We have used integrated accelerograms from four TERRAscope stations at distances between 70 and 150 km. The earthquake process consists of unilateral rupture propagation, 3 km/s, on two distinct segments with different strikes: N10°W and N40°W. The two segments are 20 and 30 km long with constant slip of 3.5 m and 5.2 m, respectively. The excitation of surface waves, resulting from a low‐velocity surficial layer, plays a critical role in matching the synthetic waveforms to the observed displacements. The displacements, due to both body waves and surface waves, are strongly affected by directivity. Matching the synthetics to the data requires a one second delay between the end of rupture on the first segment and the initiation of rupture on the second segment. The seismic moment of the subevents are 2.8 × 1019N‐m and 8.4 × 1019N‐m, leading to a total moment of 1.12 × 102

ISSN:0094-8276    

DOI:10.1029/92GL02822

年代:1993

数据来源: WILEY

摘要:

This paper describes a collaborative GPS‐Project to determine recent crustal movements and deformations across the NE Ionian Sea. This region is characterized by rifting in the African Foreland (Pelagian Sea), subduction along the Calabrian and West Hellenic Arcs, rotation of the Italian peninsula and distributed normal faulting in Central Greece. From GPS‐campaigns on the Ionian Islands and in NW Greece performed in 1989 and 1991 a kinematic field is deduced which is controlled by the deep trough following the NW coast of Kephalonia island. It is concluded that this prominent bathymetric feature resembles an active fault system (Kephalonia fault) which has the signature of a right‐lateral transform

ISSN:0094-8276    

DOI:10.1029/93GL00532

年代:1993

数据来源: WILEY

摘要:

In the central part of the New Hebrides island arc a sizable gap exists in the seismic activity. Seismic observations in the zone of the gap have been previously interpreted as either related to a detachment of part of the downgoing slab or associated with a continuous slab. We give a geometrical argument which, added the seismic observations from these previous studies, adds one step in favor of the detachment hypothesis. After unfolding the downgoing plate and restoring it to its initial state, using a 3D balance technique, we show that the gap can be filled with three pieces. Two of these pieces are seismic zones located beneath the seismic gap and the third one is a deep (550 – 650 km) seismic zone located about 200 km north‐east of the arc. These three pieces could be detached parts of the subducting pl

ISSN:0094-8276    

DOI:10.1029/93GL00681

年代:1993

数据来源: WILEY

摘要:

Compaction‐driven fluid flow in accretionary prisms is ineffective in changing heat flow across the lower slope, even when the rate of fluid flow is greatly enhanced by hydrofracturing, as results of numerical analysis show. For most faults which are long relative to their thickness, conductive heat loss to the wall rock is much more effective in heat transport than advective transport along the fault

ISSN:0094-8276    

DOI:10.1029/93GL00331

年代:1993

数据来源: WILEY

摘要:

The quality factor Q has been measured in the Pacific ocean along many paths using long period seismograms of the Geoscope and IDA networks. The Love and Rayleigh phase velocity and QR−1have been regionalised in the period range 60s to 200s, and then simultaneously inverted at depth to obtain 3D images of S‐wave velocity and attenuation Qβ−1in the depth range 60–300km. Up to 100s, three very attenuating zones appear, one under the East Pacific Rise (E.P.R), another one around Hawaii, a third one east of Kermadec. By inversion, those three anomalies are found stable down to 160km. Below 200km, lateral variations are less intense and differently distributed; the maximum attenuation seems to concentrate along a northeast trend in the North Central

ISSN:0094-8276    

DOI:10.1029/93GL00296

年代:1993

数据来源: WILEY

摘要:

Recent dating of geomagnetic field reversals over the past 2 Ma, by both the radiometric and astrochronologic techniques, indicates that the K‐Ar derived ages for these reversals are too young. We report herein on40Ar/39Ar incremental heating study of two geomagnetic field reversals trapped in lavas on Akaroa Volcano, New Zealand, that demonstrate that the K‐Ar derived ages for field reversals at 10–9 Ma are too young by about 7%. The new age for the termination of chron 5, a critical tie point on the geomagnetic polarity time‐scale for late Miocene time, is 9.67

ISSN:0094-8276    

DOI:10.1029/93GL00332

年代:1993

数据来源: WILEY

摘要:

Accurate and detailed paleomagnetic data can be obtained from continuous measurements of U‐channels extracted from sedimentary cores using a small‐diameter pass‐through magnetometer and high resolution signal‐response pick‐up coils. The spatial resolution is not significantly lower than that obtained by measuring standard paleomagnetic samples and features on the order of 3–5 cm can be confidently resolved. We propose a method to analyze the demagnetization data based on the angular dispersion of the directions between successive demagnetization steps and the downcore changes in the rate of intensity decrease. This technique allows us to distinguish very rapidly between intervals with well‐identified characteristic magnetic components and zones characterized by a more complex behavior during demagnetization. It is also possible to directly measure the magnetic susceptibility, and to induce and measure most rock magnetic properties along the U‐channels. Thus all parameters necessary for a complete paleomagnetic study of sediment cores can be confidently obtained directly from U‐channels without extracting individual samples. Finally this equipment makes possible the measurement and complete demagnetization of up to 10 single samples at a time in less than one hour by using techniques similar to those developed f

ISSN:0094-8276    

DOI:10.1029/93GL00213

年代:1993

数据来源: WILEY

摘要:

The temperature dependence of magnetic domain pattern in titanomagnetite and titanohematite of self‐reversing andesites from the 1985 eruption of the Nevado del Ruiz volcano (Colombia) has been observed using the Bitter technique. During heating/cooling cycles in the laboratory, the natural remanent magnetization loses the self‐reversal properties between 110°C and 180°C. The titanohematite domains disappear in the same temperature interval. Large grain regions without visible colloid contrast are observed between room temperature and 180°C. Utilizing the high resolution of a magnetic force microscope, it is found that these regions contain either domains with wall spacing of about 3 µm or a buckling pattern. Along the phase boundary between a titanomagnetite and a titanohematite grain but within the titanohematite, a 2 µm wide chemically different domain has been observed. It has a higher iron content than the main titanohematite. The two titanohematite phases represent two phases with higher Curie temperature, Tc, but lower spontaneous magnetization, Ms, and lower Tcbut higher Ms, respectively. Negative interaction between these phases is called upon to explain the self‐reversing

ISSN:0094-8276    

DOI:10.1029/93GL00533

年代:1993

数据来源: WILEY